Deque: Stack overflow when exceeding 17_000 elements

[luc-blaeser]

The Deque implementation currently causes a stack overflow trap when using it at larger scale, e.g. by inserting more than 17_000 elements and then removing those from the other end of the deque.

Example of failure, by extending dequeTest.mo:

ignore Iter.toArray(iterateBackward(populateForward(1, 17_000)));

This is due to the internally used List.split() function that involves non-optimized tail recursion.

Related possible improvement for Deque:

• Reduce runtime and space performance of push/pop functions to O(1) worst-case per single function call (by avoiding List-split implementation).